This report presents results of the National Assessment of Educational Progress (NAEP) 2005 science assessment. In addition to national results for grades 4, 8, and 12, fourth- and eighth-grade results are reported for 44 participating states and the Department of Defense schools. Assessment results are described in terms of students’ average science score on a 0–300 scale and in terms of the percentage of students attaining each of three achievement levels: Basic, Proficient, and Advanced. National scores at selected percentiles on the scale (indicating the percentage of students whose scores fell at or below a particular point) are also discussed, as are scores for three fields of science. This report also provides results for groups of students defined by various background characteristics (e.g., gender, race/ethnicity, and students’ eligibility for free/reduced-price school lunch). Comparisons are made to results from previous years in which the assessment was administered. In addition to the 2005 results, national results are reported from the 1996 and 2000 assessments. The national results show an increase in the average science score since 1996 at grade 4, no significant change at grade 8, and a decline at grade 12. Results for participating states and other jurisdictions from the 2000 assessment at grade 4 and from the 1996 and 2000 assessments at grade 8 are also reported. Of the 37 states and jurisdictions that participated in both the 2000 and 2005 fourth-grade science assessments, nine showed gains in average scores and none showed declines. Of the 37 states and jurisdictions that participated in the 2000 and 2005 eighth-grade assessments, 11 showed gains and 4 showed declines. The report also includes sample assessment questions and examples of student responses. A page of technical notes provides information about sampling, statistical significance, use of accommodations, and school and student participation.